Location: Starting from the serving cell
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- Category: Articoli
- Published on Wednesday, 10 April 2013 21:05
It is obvious to think about approaches used for the location by means of mobile network when someone wants to determine if a specific mobile device was or not in a determined space and at a given moment. For this reason, as already written in my paper published in Sicurezza & Giustizia magazine, the tools for the data extraction from mobile phones/smartphones are used, hoping to locate the registration of GPS positions (WiFi, geolocalized photo and/or Video) together with call detail record in order to acquire information about the position of the Base Transceiver Station and about the theoretical electromagnetic coverage of the hosted cells. In addition, the theoretical coverage of the cells, supplied by telephone service providers, can be narrowed through the statistical detection of the coverage using a frequency scan of mobile phone network (I have personally used TeMS by Ascom).
Actually, location tools and methods can have a symmetrical application. It is frequent, in fact, the need to know who was, or better which mobile device was in a determined space and at a given moment.
In order to do this, it is necessary to ask telephone service providers which cells cover a determined area, square or street. Unfortunately, telephone service providers supply vague information based on a series (often long) of cells that potentially cover the area of interest.
The frequency scan of mobile phone network allow, however, to detect among the cells with theoretical coverage of the area of interest the actual serving cell. The detection of the coverage area have a statistical quality and so it has to be realized on a number of measurements that represents a useful statistical sample collected on different days, times with particular attention to the time in which the event, under technical investigation, occurred. In some lucky cases, if a long time has not passed since when the event occurred it is likely that the mobile network supplied by the telephone service provider has not undergone changes.
The absence of any changes needs, however, to be verified in order to determine that the fulfillment of the detection has been realized taking into consideration the configuration of the mobile network which would have to be very similar to that of the event under investigation, otherwise the proof will not be valid.
This is a very complex situation and we will talk about it on another occasion.
Another important thing to verify is the high confluence of the located serving cell in order to exclude the possibility that the mobile network was forced to change the priority of selection and reselection of the serving cell due to the traffic. This is a very complex situation and we will talk about it on another occasion.